Polymeric binders having specific peel and cure properties and useful in making creped webs

ABSTRACT

This invention is directed to alkylphenol ethoxylate (APE)-free polymer binders formed by aqueous free radical emulsion polymerization and having specific peel and cure properties. The APE-free polymeric binders have a peel value, when adhered to a heated metal surface, of 35% to 200% of the peel value shown by a standard APE-based polymer binder control and exhibit a cure profile such that at least 55% cure is achieved within 30 seconds at a temperature required for cure, and a wet tensile strength at 30-seconds of cure of at least 1000 g/5 cm. Wet tensile strength is used as a measure of cure. Binders having the peel and cure properties described herein can be considered for use in crepe processes, especially DRC processes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/999,660, filed on Nov. 30, 2004, which is a continuation ofU.S. patent application Ser. No. 10/025,114, filed on Dec. 19, 2001, nowU.S. Pat. No. 6,824,635 B2, issued Nov. 30, 2004, both of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

Crepe processes, especially double recrepe (DRC) processes, have beenused to produce paper products, such as paper towels and wipes, withspecific properties. The DRC process involves creping a base sheet ornonwoven web on a drum, printing a polymeric binder on one side of thesheet, flash drying the binder, creping the base sheet on a drum again,printing a polymeric binder on the other side of the base sheet, flashdrying the binder, and then creping the base sheet a third time. Thebase sheet is printed while traveling through gravure nip rolls. Variouscrepe processes and binding materials used in the processes are known.Examples of such processes are disclosed in U.S. Pat. No. 3,879,257,U.S. Pat. No. 3,903,342, U.S. Pat. No. 4,057,669, U.S. Pat. No.5,674,590, and U.S. Pat. No. 5,776,306.

In order for the base sheet or web to adhere adequately to the crepingdrum, polymeric binders used in creping processes are typically emulsionpolymers containing surfactants that are based on alkylphenolethoxylates (APEs). Known emulsion polymeric binders, that are free ofalkylphenol ethoxylates, have not been effective in creping processes,especially DRC processes, because they do not provide the necessaryadhesion to creping drums, produce an unacceptable amount of foam, aretoo low in viscosity, decompose at elevated temperatures causing anunacceptable odor, do not give acceptable tensile performance, and/orare subject to felt filling.

Appropriate binders for making paper products using a crepe processshould be free of APE-based surfactants, adhere to a creping drum,provide a high degree of softness and absorbency to the finishedproduct, provide acceptable tensile strength, and not felt-fill.

Heretofore, specific measurable properties for predicting theeffectiveness of binders for a crepe process have not been reported.

BRIEF SUMMARY OF THE INVENTION

This invention is directed to APE-free polymer binders formed byemulsion polymerization techniques and having a specific peel value anda specific cure profile. Binders having the peel value and cure profiledescribed herein can be considered for use in crepe processes,especially DRC processes. According to this invention, the APE-freepolymeric binders have a peel value, when adhered to a heated metalsurface, of 35% to 200% of the peel value shown by a standard APE-basedpolymer binder control (i.e., AIRFLEX® 105 vinyl acetate-ethylene (VAE)polymer emulsion) and exhibit a cure profile such that at least 55% cureis achieved within 30 seconds at a temperature required for cure. Thepeel value is determined by a modified release and adhesion test.

Wet tensile strength is used to determine the cure profile. Cure isdescribed herein as reacting under time, temperature and catalyticconditions to produce a maximized performance level of the binder. Theconditions used to simulate cure involve a temperature of about 320° F.(160° C.), an acid catalyst at about a 1% level based on the solidscontent of the binder, and time, in seconds, up to 180 seconds (3minutes). The cure rate profile can be plotted by measuring wet tensilestrength of bonded nonwoven substrates at various levels of cure time.It is desirable that the cured material reaches at least 55% of itsultimate wet tensile properties at 30 seconds of cure. The cure profileis dependent on time, temperature, and catalysis. Those variables can bevaried to meet the requirements of performance. For instance, one coulduse less time and higher temperature or catalyst. Also, one could use nocatalyst and rely on temperature or time to provide the needed cure. Ithas been shown that lower cure temperatures and other reaction routesare also capable of providing acceptable levels of performance.Temperatures as low as 200° F. (93° C.) have been shown to be acceptablefor producing effective products as determined by finished wet tensilestrength.

Binders having the properties described above are excellent candidatesfor use in crepe, especially DRC, processes. When used in making paperproducts, they should adhere to the creping drum providing a high degreeof softness and absorbency to the finished paper product and notfelt-fill; thus reducing production breaks, while ensuring that thedesired finished product performance is manufactured.

DETAILED DESCRIPTION OF THE INVENTION

Any APE-free polymer prepared according to well known emulsionpolymerization techniques and manifesting the requisite cure profile andpeel value is suitable in this invention.

APE-free polymer emulsions can be formed by polymerizing one or moreethylenically unsaturated monomers and optionally one or morecrosslinking monomers, under emulsion polymerization conditions, in thepresence of a combination of a specific anionic surfactant and aspecific nonionic surfactant, wherein said anionic surfactant is asodium laureth sulfate having 1 to 12 moles of ethylene oxide, saidnonionic surfactant is a secondary alcohol ethoxylate containing 7 to 30moles of ethylene oxide or an ethoxylated branched primary alcoholcontaining 3 to 30 moles of ethylene oxide, said primary or secondaryalcohol containing 7 to 18 carbons

Ethylenically unsaturated monomers that can be used in the preparationof the polymer emulsions of this invention include, but are not limitedto, vinyl esters, such as vinyl acetate, ethylene, styrene, butadiene,C₁₋₈ alkyl esters of acrylic and methacrylic acid, such as methyl(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl(meth)acrylate, 2-ethylhexyl (meth)acrylate, diacrylates, unsaturatedcarboxylic acid, such as acrylic, methacrylic, crotonic, itaconic, andmaleic acid, acrylonitrile, and vinyl esters of C₂₋₁₀ alcohols.

The polymer can contain up to 10% of one or more crosslinking monomers.Examples of crosslinking monomers are N-(C₁₋₄) alkylol (meth)acrylamide,such as N-methylol acrylamide, i-butoxy methylacrylamide,acrylamidoglycolic acid, acrylamidobutyraldehyde, and the dialkyl acetalof acrylamidobutyraldehyde in which the alkyl can have 1 to 4 carbons.Any of the crosslinking monomers can be used alone, together, or incombination with acrylamide.

Polymer emulsions comprising 50 to 90 wt % (preferably 70 to 85 wt %)vinyl acetate, 5 to 44 wt % (preferably 10 to 30 wt %) ethylene, and 1to 10 wt % (preferably 3 to 8 wt %) one or more crosslinking monomer,based on the total weight of monomers, can be formed using thesurfactant package described herein.

The emulsion polymerization may be conducted in a stage or sequentialmanner and can be initiated by thermal initiators or by a redox system.A thermal initiator is typically used at temperatures at or above about70° C. and redox systems are preferred at temperatures below about 70°C. The amount of thermal initiator used in the process is 0.1 to 3 wt %,preferably more than about 0.5 wt %, based on total monomers. Thermalinitiators are well known in the emulsion polymer art and include, forexample, ammonium persulfate, sodium persulfate, and the like. Theamount of oxidizing and reducing agent in the redox system is about 0.1to 3 wt %. Any suitable redox system known in the art can be used; forexample, the reducing agent can be a bisulfite, a sulfoxylate, ascorbicacid, erythorbic acid, and the like. Examples of oxidizing agent arehydrogen peroxide, organic peroxides, such as t-butyl peroxide ort-butyl hydroperoxide, persulfates, and the like.

Effective emulsion polymerization reaction temperatures range from about50 and 100° C.; preferably, 75 to 90° C., depending on whether theinitiator is a thermal or redox system.

The specific combination of anionic and nonionic surfactants for theemulsion polymerization process has been shown to produce crosslinkingpolymer emulsions that are effective as binders in a creping process,especially a DRC process. The anionic surfactant is a sodium laurethsulfate having 1 to 12, preferably 2 to 5, moles of ethylene oxide. Anexample of an appropriate anionic surfactant is Disponil FES 32 IS(sodium laureth sulfate containing 4 moles of ethylene oxide), suppliedby Cognis as a 30% aqueous solution. The nonionic surfactant is asecondary alcohol ethoxylate, such as 2-pentadecanol ethoxylate,containing 7 to 30 moles, preferably 12 to 20 moles, of ethylene oxideor an ethoxylated branched primary alcohol, such as tridecanolethoxylate, containing 3 to 30 moles, preferably 9 to 20 moles, ofethylene oxide. The primary or secondary alcohol can contain 7 to 18,preferably 9 to 14 carbons. An example of an appropriate nonionicsurfactant is Tergitol 15-S-20 (a secondary alcohol ethoxylatecontaining 20 moles of ethylene oxide), supplied by Dow as an 80%aqueous solution.

The amount of active surfactant, based on total polymer, can be 1 to 5wt % (preferably 1.5 to 2 wt %) for the anionic surfactant and 0.25 to 5wt % (preferably 0.5 to 1.5%) for the nonionic surfactant. The weightratio of anionic to nonionic surfactant can range from 4:1 to 1.5:1. Aweight ratio of 65:35 (anionic:nonionic surfactant) has been found togive a latex that provides appropriate adhesion to creping drums, has amoderate viscosity with little foam generation, results in lessoff-gassing than APE-based latexes, and has an accelerated sedimentationof no greater than 1%.

The peel value of prospective polymeric binders for use in crepeprocesses, especially DRC processes can be measured using the followingadhesion and release procedure:

Attach a 2-inch×6-inch× 1/32-inch stainless steel plate to a movableheated (270° F.; 132° C.) inclined (for example, 45° angle) metalplatform and allow the plate to equilibrate to the temperature of theplatform (˜2 minutes.) Apply approximately 0.42 g of the polymeremulsion to a 1½-inch×6-inch piece of bleached, mercerized cottonpoplin. Attach the jaws of a Testing Machine, Inc. gram tensilemeasuring apparatus to one of the long ends of the cotton poplin. Pressthe coated side of the coated cotton poplin onto the heated stainlesssteel plate with a 3-pound lab roller by rolling the lab roller back andforth over the substrate for 10 seconds. After 30 seconds, move thestainless steel plate away from the tensile measuring device (to whichthe substrate is attached) at a rate of 12 inches/minute (30.48cm/minute). Record the amount of force needed to remove the cotton fromthe stainless steel plate and compare it to AIRFLEX 105 VAE emulsioncontrol.

The AIRFLEX 105 polymer emulsion can be prepared in small batches asfollows: Initially charge a one-gallon, stirred, stainless steelreaction vessel with 883.5 g of deionized water, 305 g of Polystep OP-3Ssurfactant mixture (20% active) of octylphenol ethoxylate (3 moles) andsodium sulfate salt of octylphenol ethoxylate (3 moles), supplied byStefan, 0.91 g of sodium citrate, 3.5 g of 50% aqueous citric acid, 2.3g of 5% aqueous ferric ammonium sulfate, and 312.0 g of vinyl acetate.While stirring, introduce 240.09 of ethylene below the surface of theliquid in the reaction vessel in order that the interpolymers have avinyl acetate:ethylene ratio of about 80:20. Heat the reaction vessel to50° C. Upon equilibration, add the following four aqueous solutionsintermittently to the reaction vessel over the course of the reaction(on a delay basis); 15% sodium formaldehyde sulfoxylate (SFS), 3.0%t-butylhydroperoxide (t-bhp), 1246.0 g of vinyl acetate and 324.0 g of a30% aqueous solution of N-methylol acrylamide (NMA). After three hours,terminate the vinyl acetate delay. Complete the NMA delay after fourhours, and continue the other two delays for another 30 minutes.Terminate the reaction by cooling.

The cure profile is determined by measuring wet tensile strength. Thefollowing procedure can be followed:

A 2-inch×6-inch unbonded DRC basesheet at about 65 gsm basis is coatedwith a binder and the binder is cured at 320° F. (160° C.) for 30seconds and for 180 seconds. The cup of a Finch Wet Strength apparatusfrom Thwing-Albert, Philadelphia, is filled with an aqueous solutioncontaining approximately 1% active Aerosol OT-75 wetting surfactant(from Cytec Industries). The cured coated basesheet is then placedaround the bar on the Finch cup attachment and the two long ends of thesample are clamped to the top jaw. The Finch cup holder is pulled overthe middle of the coated basesheet and the coated basesheet is allowedto soak in the aqueous surfactant solution for 15 seconds. The coatedbasesheet is then pulled away from the bar until the basesheet breaks.The force required to break the basesheet is recorded. If the wettensile strength of the bound basesheet cured for 30 seconds is at least75% the wet strength of the 180-second cured bound basesheet, the binderwill not felt-fill due to insufficient cure. For purposes of evaluatingbinders for use in a crepe process, at least 55% of the ultimate wettensile strength is achieved within 30 seconds at the cure temperature.

There is a minimum level of wet tensile performance that needs to beattained to produce a nonwoven fabric that can perform its intendedfunctions; for example, a towel or wipe. For this invention, at a binderadd-on of 3 to 20% (preferably 5 to 15%), the cured polymer binder ontoa suitable cellulosic substrate should provide a minimum wet tensilestrength of 1000 g/5 cm at 30 seconds at cure temperature. In anotherembodiment the minimum wet tensile strength at 30 seconds at curetemperature is at least 1500 g/5 cm.

Polymer binders that show a peel value of 35% to 200% (preferably 50% to125%) of AIRFLEX 105 VAE emulsion control and a cure profile in which atleast 55% of the ultimate wet strength is achieved in 30 seconds at thecure temperature, are considered important candidates as binders for acrepe process, especially a DRC process.

To be used in a crepe process, especially a DRC process, the polymeremulsions identified by the peel and cure tests described above, shouldhave a viscosity of 5 to 80 cps at about 30% solids, and should becapable of being thickened to 100 cps with a thickener, such as ahydroxyethyl cellulose-based thickener. Viscosity is measured using aBrookfield viscometer, Model LVT, spindle #3 at 60 rpm. The emulsionpolymers of this invention should also be stable at temperatures up toabout 550° F. (288° C.). The polymer emulsions should produce a minimalamount of foam when pumped and beaten during a DRC process.

Binders identified by this invention can be used in crepe processes wellknown in the art. Examples of crepe processes are described in thepublications listed in the “Background of the Invention” section of thespecification. Nonwoven webs typically used in a crepe process are woodpulp (alone or blended with natural or synthetic fibers) processed by adry (air-laid, carded, rando) or wet-laid process.

The amount of binder applied to the web can vary over a wide range; forexample, about 5 to 40%; preferably 10 to 35% of the finished product.When the products are wiper products, it is desirable to keep the amountto a minimum.

The invention will be further clarified by a consideration of thefollowing examples, which are intended to be purely exemplary of the useof the invention.

EXAMPLE

Emulsion polymerization of vinyl acetate, ethylene, and N-methylolacrylamide was carried out in presence of various surfactant systems ina one-gallon stirred, stainless steel reaction vessel equipped with ajacket. In Run 1, reaction vessel was charged initially with 883.5 g ofdeionized water, 126.75 g of Disponil FES 32 IS, 25.625 g of Tergitol15-S-20, 0.91 g of sodium citrate, 3.5 g of 50% aqueous citric acid, 2.3g of 5% aqueous ferric ammonium sulfate and 312.0 g of vinyl acetate.While stirring, 240.0 g of ethylene was introduced below the surface ofthe liquid in the reaction vessel in order that the interpolymers wouldhave a vinyl acetate:ethylene ratio of about 80:20. The reaction vesselwas heated to 50° C. Upon equilibration, the following four aqueoussolutions were intermittently added to the reaction vessel over thecourse of the reaction (on a delay basis); 15% sodium formaldehydesulfoxylate (SFS), 3.0% t-butylhydroperoxide (t-bhp), 1246.0 g of vinylacetate and 324.0 g of a 30% aqueous solution of N-methylol acrylamide(NMA). After three hours, the vinyl acetate delay was terminated. Afterfour hours the NMA delay was complete and the other two delays continuedfor another 30 minutes. The reaction was terminated by cooling.

Using the same emulsion recipe as Run 1, several surfactant packageswere examined. The viscosity, emulsion stability, acceleratedsedimentation, peel (% of AIRFLEX 105 VAE emulsion control), and30-second wet tensile strength (% of ultimate wet tensile strength) weremeasured.

Viscosity was measured using a Brookfield viscometer, Model LVT, spindle#3 @ 60 rpm and 77° F. (25° C.), at about 24 hours after preparation toallow for cooling and the finishing of any residual-free monomer.

Emulsion stability was measured by measuring the viscosity at 4intervals: after forming the polymer emulsion; after 3 days in a 120° F.oven; after 1 week in a 120° F. oven; and after 2 weeks in a 120° F.oven.

Accelerated sedimentation was measured by taking a sample of product anddiluting it in half with water, spinning it in a centrifuge for fiveminutes at a predetermined setting, e.g., 2800 rpm±100, and measuringthe amount of precipitate forced to the bottom of the tube. When aone-gallon reactor is used, an accelerated sedimentation higher than 1%is considered unsatisfactory. However in a plant-size operation, up toabout 3% is acceptable.

The peel value and the wet tensile strength of each of the binders weredetermined as described above.

The results of the tests are presented in the tables below: TABLE 1Ratio of Peel 30-second Anionic Accelerated Value wet tensile AnionicNonionic to % Viscosity, Sedimentation, (% (% of Run surfactantsurfactant Nonionic Solids cps % control) ultimate) 1 Disponil Tergitol1.86 52.9 660 1.0 100 79.4 FES 32 IS 15-S-20 2 B-330S Tergitol 1.86 53.2532 4.0 47 70.0 15-S-20 3 Rhodapex Tergitol 1.86 53.2 632 2.5 73 no dataES 15-S-20 4 FES 993 Tergitol 1.86 53.1 160 8.0 57 60.9 15-S-20 5 Steol4N Tergitol 1.86 53.1 348 2.0 48 66.6 15-S-20 6 Texapon Tergitol 1.8653.2 152 6.0 75 92.9 NSO 15-S-20 7 Disponil Disponil 1.86 53.3 600 3.0175 78.4 FES 32 IS 3065 8 Disponil Disponil 1.86 53.3 490 4.0 200 72.6FES 32 IS 1080 9 Disponil TD-3 1.86 53.0 318 2.0 110 no data FES 32 IS10 DOSS Tergitol 1.86 57.0 86 1.0 135 47.3 15-S-20 11 DOSS Tergitol 153.4 372 0.5 100 34.2 15-S-20 12 DOSS Tergitol 3 53.1 54 1.0 35 35.715-S-20 13 DOSS Tergitol 0.33 53.3 116 0.5 130 43.7 15-S-20 14 DOSSTergitol 0.67 60.3 474 1.5 105 84.8 15-S-20 15 Tergitol Tergitol 2 55.8600 10 68 72.1 15-S-3 15-S-20 sulfate 16 DOSS Tergitol 0.67 60.5 228 3.590 61.4 15-S-3 17 EST-30 Makon 2 54.2 810 1.5 67 78.7 TD-3Disponil FES 32 IS = sodium laureth sulfate containing 4 moles ofethylene oxide, supplied by CognisTergitol 15-S-20 = a secondary alcohol ethoxylate containing 20 moles ofethylene oxide, supplied by DowB-330S = sodium laureth sulfate (3 moles) supplied by StepanRhodapex ES = sodium laureth sulfate (3 moles) supplied by RhodiaFES 993 = sodium laureth sulfate (1 mole) supplied by CognisSteol 4N = sodium laureth sulfate (4 moles) supplied by StepanTexacon NSO = sodium laureth sulfate (2 moles) supplied by CognisDOSS = dioctyl sulfosuccinateTergitol 15-S-3 Sulfate = secondary alcohol ethoxylate sulfate (3 moles)supplied by DowEST-30 = sodium trideceth sulfate (3 moles) supplied by RhodiaDisponil 3065 = lauryl alcohol ethoxylate (30 moles) supplied by CognisDisponil 1080 = lauryl alcohol ethoxylate (10 moles) supplied by CognisMakon TD-3 = tridecyl alcohol ethoxylate (3 moles) supplied by Stepan

TABLE 2 30 Second Cure Dry Wet Wet/Dry Wet Tensile, Time, Tensile,Tensile Tensile % of Run seconds g/5 cm g/5 cm Ratio Ultimate 1 30 44982153 47.9 79.4 1 180 4965 2713 54.6 8 30 4023 2139 53.2 72.6 8 180 47382945 62.2 10 30 4219 1822 43.2 47.3 10 180 5296 3849 72.7 12 30 43181301 30.1 35.7 12 180 5346 3648 68.2 15 30 4861 2433 50.1 72.1 15 1805003 3376 67.5 16 30 5029 2377 47.3 61.4 16 180 5249 3873 73.8

The peel value and wet tensile data in Table 1 show that the binders ofRuns 1-2, 4-8, and 14-17 can be considered for use as binders in crepeprocesses, especially DRC processes. The binders of Runs 10-13 would beinappropriate for consideration as potential binders in crepe processesbecause the 30-second wet tensile strength is less than 55% of theultimate wet tensile strength of the binder. Without cure data, Runs 3and 9 are the questionable for use in a crepe process. The data in Table2 show that, although the bonded product of Runs 10 and 12 has a wettensile greater than 1000 g/5 cm at 30 seconds of cure time, the % ofultimate at 30 seconds is less than 55%. These data confirm that thebinder of Runs 10 and 12 would not be appropriate for crepe processes.

1. In a polymer binder used in a crepe process that comprises applyingsaid polymer binder to a nonwoven web, drying, and creping the nonwovenweb on a creping drum, the improvement which comprises an alkylphenolethoxylate free aqueous polymer emulsion binder formed by aqueous freeradical emulsion polymerization of one or more ethylenically unsaturatedmonomers and one or more crosslinking monomers, said binder having apeel value of 35% to 200% of a standard alkylphenol ethoxylate-basedvinyl acetate-ethylene polymer emulsion control, a cure profile in which55% cure is achieved within 30 seconds of being exposed to a temperaturerequired for cure, and a wet tensile strength at 30-seconds of cure ofat least 1000 g/5 cm.
 2. The polymer binder of claim 1 wherein the oneor more crosslinking monomer is selected from the group consisting of anN-alkylol acrylamide, an N-alkylol methacrylamide, i-butyoxymethylacrylamide, acrylamidoglycolic acid, acrylamidobutyraldehyde, anda dialkyl acetal of acrylamidobutyraldehyde, wherein alkyl is 1 to 4carbons.
 3. The polymer binder of claim 2 wherein the peel value is 50to 125% of the polymer emulsion control.
 4. The polymer binder of claim2 wherein the wet tensile strength at 30 seconds of cure is at least1500 g/5 cm.
 5. In a polymer binder used in a double recrepe processwherein the recrepe process comprises applying said polymer binder toone side of a nonwoven web, drying, and creping the nonwoven web on acreping drum, followed by applying said polymer binder to the oppositeside of the nonwoven web and again, drying, and creping the nonwoven webon a creping drum, the improvement which comprises an alkylphenolethoxylate free aqueous polymer emulsion binder formed by aqueous freeradical emulsion polymerization of one or more ethylenically unsaturatedmonomers and one or more crosslinking monomers, said binder having apeel value of 35% to 200% of a standard alkylphenol ethoxylate-basedvinyl acetate-ethylene polymer emulsion control, a cure profile in which55% cure is achieved within 30 seconds of being exposed to a temperaturerequired for cure and a wet tensile strength at 30-seconds of cure of atleast 1000 g/5 cm.
 6. The polymer binder of claim 5 wherein the one ormore crosslinking monomer is selected from the group consisting of anN-alkylol acrylamide, an N-alkylol methacrylamide, i-butyoxymethylacrylamide, acrylamidoglycolic acid, acrylamidobutyraldehyde, anda dialkyl acetal of acrylamidobutyraldehyde, wherein alkyl is 1 to 4carbons.
 7. The polymer binder of claim 5 having a viscosity of 5 to 80cps at about 30% solids.
 8. The polymer binder of claim 5 wherein thepeel value is 50 to 125% of the polymer emulsion control.
 9. The polymerbinder of claim 5 wherein the wet tensile strength at 30 seconds of cureis at least 1500 g/5 cm.